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Area numbers - The first three numbers originally represented the state in which a person first applied for a Social Security card. Numbers started in the northeast and moved westward. This meant that people on the east coast had the lowest numbers and those on the west coast had the highest. Since 1972, the SSA has assigned numbers and issued cards based on the ZIP code in the mailing address provided on the original application form. Since the applicant's mailing address doesn't have to be the same as his residence, his area number doesn't necessarily represent the state in which he resides. For many of us who received our SSNs as infants, the area number indicates the state we were born in. You can find out which area numbers go with each state at SSA.gov: Social Security Number Allocations.

Group numbers - These two middle digits, which range from 01 through 99, are simply used to break all the SSNs with the same area number into smaller blocks, which makes administration easier. (The SSA says that, for administrative reasons, group numbers issued first consist of the odd numbers from 01 through 09, and then even numbers from 10 through 98, within each area number assigned to a state. After all the numbers in group 98 of a specific area have been issued, the even groups 02 through 08 are used, followed by odd groups 11 through 99.)

Serial numbers - Within each group designation, serial numbers -- the last four digits in an SSN -- run consecutively from 0001 through 9999.

Although SSNs are issued in some order, there is no simple way to tell a person's age based on his Social Security number.